Towards chip-scale optical frequency synthesis based on optical heterodyne phase-locked loop.

Area of Science:

• Photonics
• Integrated Optics
• Optical Communications

Background:

• Optical phase-locked loops (OPLLs) are crucial for frequency control in optical systems.
• Integrated photonic circuits offer miniaturization and enhanced functionality for OPLLs.

Purpose of the Study:

• To design and demonstrate an integrated heterodyne OPLL using indium phosphide (InP) photonic integrated circuits.
• To achieve arbitrary frequency synthesis and fast frequency switching of an on-chip laser.
• To evaluate the phase noise performance of the integrated OPLL system.

Main Methods:

• Utilized an InP photonic integrated circuit and commercial electronic components.
• Employed a microresonator-based optical frequency comb as the input reference signal.
• Implemented an offset-locked, widely-tunable sampled-grating distributed-Bragg-reflector laser.
• Demonstrated frequency synthesis by tuning the radio frequency (RF) offset source.

Main Results:

• Achieved arbitrary frequency synthesis with better than 100 Hz tuning resolution and ± 5 Hz accuracy.
• Demonstrated frequency switching to over two dozen comb lines (~5.6 nm) in approximately 200 ns.
• Obtained a low residual phase noise of -80 dBc/Hz at a 200 Hz offset.

Conclusions:

• The integrated heterodyne OPLL system successfully demonstrates precise frequency control and rapid switching capabilities.
• The developed InP-based photonic integrated circuit is a promising platform for advanced optical frequency synthesis and control.
• The low phase noise performance indicates suitability for demanding optical communication and signal processing applications.